1. Field of the Invention
The present invention relates to a control system for a hybrid vehicle driven by an engine and a motor, and more particularly, relates to a control system, capable of recovering a charge and discharge balance during travelling when the charge and discharge balance of the storage battery is tend to converted to the over discharge state.
2. Background Art
Conventionally, a hybrid vehicle provided with a power source consisting of a motor in addition to an engine is known. There are two types of hybrid vehicles, one is series hybrid vehicles and the other is parallel hybrid vehicles. The series hybrid vehicles are driven by motors which are driven by an output of a generator driven by the engine.
Thus, disconnection of the mechanical coupling between the engine and the vehicle wheel allows constant rotation of the engine at high gas oil ratio and low emission, and better gas oil ratio and lower emission can be obtained than the case of the conventional engine.
In contrast, in the parallel hybrid vehicles, a motor directly connected with the engine assists the engine for rotating the drive shaft, and the motor is used as a generator for charging the electric energy into the storage battery.
Thus, in the parallel hybrid vehicles, irrespective of the presence of the mechanical connection between the engine and the wheels, a better gas oil ratio and lower emission can be obtained.
There are a few types in the above-described parallel hybrid vehicles, one is a type, in which a motor, directly coupled with the engine output axis for supporting the engine output, charges the battery at the time of deceleration functioning as a generator, and the other is a type, in which both or either one of the engine and the motor can generates the driving force and the generator is additionally provided.
In the hybrid vehicles shown above, the demands of the driver can be satisfied by preserving the electric energy of the battery (hereinafter called the residual capacity) by vehiclerying out a variety of controls such that the motor assists the engine at the time of accelerating and, at the time of deceleration, the motor charges the battery by deceleration regeneration. Fr example, since a large quantity of deceleration regeneration can be obtained after the high speed travelling, the battery can retrieve a part of the consumed energy at the time of deceleration. After climbing up the mountain path, the battery can be charged afterward at the time of travelling the downhill (disclosed in Japanese Patent Application, First Publication).
However, in the above-described conventional hybrid vehicles, there are many cases, in which preservation of the deceleration regeneration is not possible, such as driving in a rapid acceleration followed by a rapid acceleration interposing a short deceleration or driving a level ground after climbing the mountain path. A problem arises that, in the former case, insufficient regeneration causes the reduction of the battery capacity during travelling, and in the latter case, the excessive battery capacity consumed in the climbing path can not be retrieved, as far as the downhill driving is not implemented.
It is therefore an objective of the present invention to provide a control system for hybrid vehicles capable of charging the battery when the residual capacity of the storage battery is tend to decrease and a predetermined value of the residual capacity has decreased from the initial read value.
The present invention according to the first aspect provide a control apparatus for a hybrid vehicle which comprises an engine for outputting a driving force of the vehicle, a motor for generating an auxiliary driving force for assisting the engine power in response to the driving condition of the vehicle, and a storage battery for storing a regenerative energy obtained by a regenerative operation of the motor at the time of supplying electric power to the motor or at the time of reducing speed of the vehicle; the control apparatus of the above-described hybrid vehicle comprises: a travel start detecting device for detecting a travel start of the vehicle; a residual capacity detecting device for detecting a residual capacity of the storage battery; an initial residual capacity comparison device for comparison of the initial residual capacity with the lower limit initial residual capacity; a lower limit threshold value setting device for setting the lower limit threshold value of the discharge quantity for said initial residual capacity; a lower limit threshold value setting device for setting the lower limit threshold value of the discharge quantity for said initial residual capacity; an upper limit threshold value setting device for setting the upper limit threshold value of the discharge quantity for said initial residual capacity; a motor control changing device for changing the control of said motor when the residual capacity of the storage battery reduces to said lower limit threshold value; and a mode setting release device for releasing the setting of the motor control mode changed by said motor control changing device when the residual capacity of the storage battery reaches said upper limit threshold value; said control apparatus further comprises: an initial residual capacity setting device for setting the initial value by assigning the lower limit initial residual value to the initial residual value when it is determined by said initial residual capacity comparison device that the initial residual capacity is lower than the lower limit threshold value.
Provision of the control apparatus of the hybrid vehicle according to the first aspect of the present invention allows to restore the residual capacity of the storage battery when it is detected that the residual capacity of the storage battery is decreased at a predetermined amount, caused by travelling without being able to acquiring sufficient regeneration energy by repeating rapid acceleration and deceleration or by travelling repeated cycles of uphill and flat without being able restoring the residual capacity of the storage battery because the reduced residual capacity caused by going uphill can not be recovered by traveling the flat.
Furthermore, according to the first aspect, since it is possible to raise the initial residual capacity by assigning the lower limit initial value for the initial residual capacity when the initial residual capacity is less than the lower limit initial value, and since the discrepancy of the initial residual capacity from the lower limit threshold value, the timing to change the control mode of the motor can be executed earlier by the motor control changing device which results in rapid restoration of the residual capacity of the storage battery.
In the control apparatus of the hybrid vehicle according to the first aspect, said control apparatus further comprises an initial value updating device for updating the upper limit threshold value and the lower limit threshold value in response to the updating the initial residual capacity by the residual capacity detected by the residual capacity detecting device when the motor control mode is released by said mode setting release device.
The structure of the control apparatus as shown above allows to update the residual capacity of the storage battery detected by the residual capacity detecting device when the residual capacity reaches the upper limit threshold value, and also allows to update the upper limit threshold value and the lower limit threshold value by the upper and lower limit threshold value setting device.
In the control apparatus of the hybrid vehicle according to the second aspect, the control apparatus further comprises an upper value comparison device for comparing the residual capacity of said storage battery with a discharge depth limiting execution upper limit, and the motor control mode is released by said mode setting release device when said upper value comparison device detects that the residual capacity of the storage battery is higher than the discharge depth limiting execution upper limit.
The above-described structure according to the third aspect allows to release the control mode of the motor rapidly, when the residual capacity of the storage battery has been restored sufficiently.
In the control apparatus of the hybrid vehicle according to any one of the first to third aspects, the change of the motor control in the case of decreasing the residual capacity of the storage battery to said lower limit threshold value corresponds to an increase of the charge quantity of the storage battery and to a change of the judgement threshold value for assisting the engine power by the motor.
The above structure allows increasing the charging amount during the cruise traveling, and increasing the frequency of the generation for recovering the discharging and charging balance by changing the assist judgement threshold value.